Search

The use of gas chromatography to measure adsorption and partition phenomena of nonelectrolytes with aqueous tetralkylammonium bromide solutions is described. Experimental details are presented, and potential sources of error are discussed. Adsorption coefficients for a series of hydrocarbons are found to be larger on the salt solutions than for water itself. Moreover, the expected increase in partition coefficients with the salt solutions relative to bulk water is shown.

The on-line coupling of a small digital computer to a liquid chromatograph is described. A new real-time language, MIRACL II, is used for programming. The experimental set-up is presented and a ndw automatic sample loop valve is described. The system has been studied in terms of the precision in peak area, peak height and retention attainable with commercial liquid chromatographic equipment. Precision in peak area and height is found to be significantly improved with the sampling valve relative to syringe injection. The influence of several pumping systems on precision was also studied and marked differences in the relative standard deviations of peak area and height were found. The relationship of the relative standard deviation of the peak area to sample size has also been studied. In addition, the important role of the flow-rate of the mobile phase on detection limits and precision is shown. Finally, some results are presented on the reproducibility of retention over short and long time periods.

Finely-ground ion exchange resin particles remove ions from solution much more rapidly than the conventional-size beads. Such finely-divided solids form suspensions when added to aqueous solutions. A method was required for rapidly removing such suspensions once ion adsorption had occurred, and to this end it is shown that the particles (-400 mesh) can be completely coagulated within a few minutes by the addition of suspensions of oppositely-charged solids. Thus anion exchange resins are coagulated by cation exchange resins (200 to 400), montmorillonite (200), kaolin (30), charcoal (10), silica (10), and glass (5), the figures representing arbitrarily defined relative coagulating abilities. Coagulating power is shown to increase markedly with decreasing particle size. Most suitable for ion removal is a mixed finely-divided resin formed by coagulation of anionic and cationic resins from pure water. The mixed resin, when added to 1 liter of 3 × 10−4 M sodium phosphate solution removes all the phosp...

The paper is a continuation of the study of the interfacial properties of water by gas chromatography. Adsorption characteristics at zero surface coverage of a large number of solutes at the gas-liquid interface of water are presented. In all cases of relatively nonpolar solutes, the differential heat of adsorption is found to be less than the heat of liquefaction, indicating the gas liquid interface of water as a low energy surface. For n-propyl ether the heat of adsorption is 4 kcal/mole higher than the heat of liquefaction, strongly suggesting hydrogen bond formation between the ethereal oxygen and the hydrogens from the water surface of the liquid. Also studied was the infinitely dilute solubility characteristics of several non-electrolytes in the thin layers of water coated on wide pore diameter adsorbents. From layer thickness of about 30 A up to 2000 A, the solubility remains constant. Finally some preliminary adsorption and 'sorption' isotherms, determined by gas chromatography, are presented. (Author)

The influence of column tubular material on column efficiency in high speed liquid chromatography has been examined. For good reproducibility in HETP, the columns were first packed dry with Corasil I (28–37μ) and then heptane saturated with 3,3′-oxydipropionitrile was flown through the column. When steady state conditions were achieved, the % loading of stationary phase was 1.1%. It was found that column materials of precision bore and seamless stainless steel, aluminum, and copper gave equivalent efficiency results for retained and unretained components. Teflon coated aluminum columns were not reproducible, in regard to HETP.

Phenylthiohydantoin derivatives of amino acids have been separated by modern liquid chromatography. The amino acid thiohydantoins were divided into three groups according to their relative polarity and three solvent systems were used to separate the groups.

In continuation of previous work on the study of water at interfaces by gas chromatography, the gas-liquid interfacial adsorption isotherms of six insoluble vapors (three n-alkanes and three branched alkanes) have been determined in the range of 4000 sq A /molecule to 500 sq A/ molecule. From these isotherms, isosteric heats of adsorption have been derived, and it has been shown that over the whole concentration range examined the isosteric heat of adsorption is equal to or less than the heat of liquefaction. This points to the fact that water is a low energy surface for hydrocarbons. The free energy of adsorption and the entropy of adsorption at constant surface coverage have been also calculated. Equations of state have been determined. Finally, calculations of thickness of the surface films indicate that the hydrocarbons can be considered to lie flat on the water surface in most cases over the whole concentration range studied. (Author)

Properties of heavily loaded columns are illustrated, especially as applied to steroid separation. By "heavily loaded" we mean that the column contains an amount of stationary phase such that the pores of the solid support are essentially filled. The solid support can be loaded with as much as 35-50% by weight of stationary liquid phase, depending on the pore volume and the activity of the solid support. Using heptane/dioxane/formamide, we studied several heavily loaded columns with different liquid loadings and solid support particles of various diameters. Porasil C (10-25 µm particle size) gave markedly improved speed and efficiency characteristics over Porasil A (44-53 µm). A separation efficiency as great as 2.5 effective plates per second was achieved with support material having the smaller particle diameter. Qualitative reasons for this good efficiency are discussed. Column efficiency was independent of quantity (from 1 µg to 1 mg) of injected steroid sample. Finally, applicability of heavily loaded columns to separation of steroids is illustrated. With stepwise pressure programming, 10 steroids can be separated in 35 min.

The use of gas chromatography for the study of the adsorption of insoluble vapors on water surfaces is described. The method involves using water coated on a porous support as packing material and presaturation of the carrier gas with water to prevent bleeding from the column. For saturated hydrocarbons it is found that the mechanism of retention is adsorption at the gas-liquid interface, whereas for aromatic hydrocarbons a mixed mechanism of adsorption and solution occurs. Contrary to results in recent literature, the differential heats of adsorption for the insoluble vapors are found to be 1 to 1.5 kcal/mol smaller than the heats of liquefaction. Possible causes for the discrepancy are examined in detail. The question of bulk water in the pores is explored via the partition coefficients of aromatic hydrocarbons. The solubilities and heats of solution are found to be close to the literature values, indicating the possibility of bulk water under the conditions of these experiments. A discussion of the advantages and disadvantages of the gas chromatographic method relative to static methods is presented.

A review of our work on the study of the interfacial properties of water by gas chromatography is presented. The theory and practice of this method is outlined, along with a critical analysis of sources of error. In this method, the retention of nonelectrolytes is measured as a function of temperature and sample size. For some solutes, adsorption at the gas-liquid interface is the only mechanism of retention, and thus one can determine thermodynamic quantities of adsorption and equations of state directly. For other solutes (e.g. aromatics) both partition and adsorption simultaneously occur, resulting in a slightly more sophisticated analysis to extract both solution and adsorption phenomena. The results indicate that water is a low energy surface to hydrocarbons. Anti-Langmuir adsorption isotherms reveal that the hydrocarbon is more attracted to itself in the liquid surface than to the water molecules. Also shown for the first time is the formation of hydrogen bond interactions between water surface molecules and Bronsted bases. (Author Modified Abstract)

The application of selective concentration by foam separation of trace species via control of charge on these species has been investigated. The removal of anionic chloro complexes of iron(III), mercury (II), and cobalt(ll) has been examined. Distribution factors, F/C, as a function of hydrochloric acid concentration have been measured with the cationic surfactant, hexadecyltrimethylammonium bromide; the trends have been found to be similar to those obtained in ion-exchange measurements, with an anionic exchanger. In the case of iron(III), F/C has also been measured as a function of surfactant concentration, initial FeCL3 concentration, and % ethanol in water. Total reflux foam separation measurements were performed for selective removal. It was found that IO-7M FeCl3 could be selectively removed in the presence of a 100-fold excess of HgCl2. Further, HgCI2 could be selectively concentrated at I M hydrochloric acid and 10-7 M in the presence of CoCl2. A model based on a mobile ion-exchanger surface is presented to explain qualitatively the trends observed.

This paper presents a critical evaluation of the method of Berezkin and Fateeva for the calculation of retention mechanism contributions to the overall retention, when several mechanisms can simultaneously occur. Using data from out laboratory of nonelectrolytes chromatographed on H2O/Spherosil XOB30 columns, it is shown that very large errors can be made in the estimation of % contribution of liquid-solid adsorption to the overall retention, using the above approach. While this mechanism undoubtedly occurs in some gas chroamtographic systems, it appears unlikely that it has the importance claimed by the above authors.

This paper continues our study on the adsorption and solution of weakly polar vapors with thin layers of water by means of gas-liquid chromatography. In particular we have examined the behavior of six new solutes: CH 2 CI 2 , CHCl 3 , CCl 4 , cis and trans -2-octene, and ethyl formate. Mixed mechanisms of retention were found for CH 2 C1 2 CHCl 3 , CCl 4 and ethyl formate, the other solutes being retained solely by adsorption. In terms of partition, good agreement has been found for static partition coefficients and heats of solution with chromatographic data, lending further evidence to the similarity of the water coated in thin layers on wide-pore diameter silica with that of bulk water. In the case of the thermodynamic quantities of adsorption at zero coverage, it has been concluded that the adsorbed state can be considered as a gaseous or mobile film in most cases. Finally, the free energy and enthalpy of adsorption per methylene group has been found to be positive when methyl formate is compared with ethyl formate.

A recycling batch foam separation apparatus has been used for the measurement of the distribution factors, Γ/c, of the anionic metal chloro complexes of iron and mercury with the cationic surfactant, hexadecyltri-methylammonium bromide. As a function of HC1 concentration, optimum values in distribution factors occur at roughly 0.3N HC1 for Hg and roughly 8N HC1 for Fe. Separations are thus possible by control of HC1 concentration.

An experimental investigation is reported of the effects of several solution parameters on the flotation of colloidal kaolin and montmorillonite using ethylhexadecyldimethylammonium bromide. The parameters examined were the zeta potential of the surfactant-particulate species, the concentration of selected cations, pH, and the ratio of initial surfactant concentration to initial particulate concentration. Two apparatuses were used to assess the affect of aggregation on flotation; one employed bubbles of 1-2 mm average diameter to effect the flotation, while the other used bubbles of about 0.2 mm. In the large bubble system, aggregation adversely affected the flotation of the particulates. For the small bubble (0.2 mm) system, the affect of aggregation on the flotation of particulates was contrary to that in the large bubble (1-2 mm) system. These observations are explained in terms of bubble sizes and their attachment to the particulate species during the flotation process. Studies also showed th...

The technique of solvent sublation has been investigated for the solutes methyl orange and rhodamine B together with the cationic surfactant, hexadecyltrimethylammonium bromide. In solvent sublation, gas bubbles generated in an aqueous phase are used to selectively extract material into a nonaqueous phase, which is immiscible with the water. Presumably attachment to the bubbles occurs through adsorption at the gas-liquid interfaces by surface-active species. The effects of parameters such as gas flow rate and concentration of surfactant on the rates of extraction of the two dyes have been investigated. Marked differences in the behavior of the dyes have been found, suggesting different mechanisms of extraction. A direct comparison has also been made between solvent sublation and solvent extraction, the latter using vigorous shaking to provide intimate contact between the liquid-liquid interfaces. Finally, the potential of solvent sublation in the separation field has been discussed.

In this article we present a general survey of adsorptive bubble separation processes. These separation methods involve the use of selective adsorption at gas-liquid interfaces, the interfaces being generated by gas bubbles in aqueous media. A variety of processes based on this mechanism have been developed, and these methods are described in this review. The underlying concepts in this field are then explored so that the similarities between the methods can be seen. Engineering applications, as well as our own work on analytical applications, are presented. Suggestions are also made as to future potentialities for these adsorptive bubble separation processes. Finally, to place these methods in proper perspective, the techniques are compared to such widely used processes as ion exchange and liquid-liquid extraction.

A simplified apparatus has been developed for the recovery and concentration of ionic species by foam fractionation. The process involves total reflux by thermal breakage of foam at the top of the column. Mechanical breakage can also be used when heat sensitive materials are used. The system has been applied to several dyes initially and then to the successful recovery of phospholipids and trace concentrations of salts of fatty acids. Solvent sublation has also been investigated as a selective separation technique. Exploratory studies indicate that the extraction process is kinetically controlled and that time might therefore be an effective separation parameter.

In continuation of our studies on the mechanism of separation of diastereoisomeric esters by gas chromatography, we have examined the gas—liquid partition behavior of a number of structurally related isomeric pairs. Differences in free energies of distribution, Δ(Δ G °), have been measured for a series of methylalkylcarbinyl a -haloalkanoates in order to investigate the effect of polar substitution of groups attached to the acidic asymmetric center. The importance of electronic effects on the acid side of the molecule on separation is further indicated through a study of meta - and para -substituted 3-methyl-2-butyl mandalates and methylalkylcarbinyl a -methylalkanoates. The influence on separation of the structure of groups attached to the alcohol side of the molecule has been studied through a series of alkylvinylcarbinyl a -acetoxypropionates. The importance of chain length of an alkyl group attached to the alcoholic asymmetric center is indicated through the chromatographic behavior of a series of a -acetoxy- and a -hydroxypropionates of secondary alcohols. Using a 150 ft. capillary column, Δ(Δ G °) values as small as −3 cal/mole have been measured. These results are interpreted in part in terms of the influence of preferred conformations of the groups attached to the asymmetric centers on the differences in gas—liquid partition behavior of the isomeric pairs.